1. Field of the Invention
The invention of this application relates generally to intravenous (IV) infusion of drugs to patients, and more particularly to aspects of an IV infusion system comprising an infusate cassette and an infusate container.
2. Description of Related Art
Mechanically controlled infusion of a liquid drug from a reservoir to a patient is a useful process of administering a drug. An electro-mechanically controlled infusion process often provides a much steadier and more accurate administration of a drug than is possible from a human giving injections. By letting a computer model determine flow rates of drug, an electro-mechanically controlled infusion device can be programmed such that the concentration of the drug at a patient's effect site compartment remains steadily within the drug's therapeutic range.
Various medical devices for controlling the infusion of a liquid directly to a patient are known. Certain of these devices utilize pumping mechanisms to deliver liquid drugs from a reservoir such as a syringe, a collapsible bag, or a vial to a patient supply tube. One example of such a device, shown in U.S. Pat. No. 6,186,977, includes a liquid drug supply in a collapsible bag and an infusion pump, which draws the drug directly from the supply and moves it along a flow passage to a patient supply tube.
Certain of these medical devices further utilize drug pump cassettes, which provide a rigid housing and pressure plate that interact with the pumping mechanisms of the devices. These cassettes serve as intermediary devices between drug containers and patient supply lines. A typical cassette includes a passage, which is acted upon by the pumping mechanism of an infusion device to move the drug along to the supply line.
One example of a cassette for use with a drug pumping system, shown in U.S. Pat. No. 6,165,154, has a fluid passage and a collapsible pressure conduction chamber for generating a pressure gradient to move drug along the passage. Certain other cassettes are known which provide means for moving drug along a flow channel. One example of this other type of cassette, shown in U.S. Pat. No. 6,202,708, provides a large chamber for mixing a powdered drug with a liquid solvent. The cassette also includes a pressure plate, which supports a fluid flow passage against which a peristaltic pump may act to move the liquid along to a patient delivery tube.
The above and other drug infusion cassettes generally have a sharp spike upon which a drug vial is impaled to provide access to the contents of the vial. Drug infusion cassettes that incorporate a sharp spike or trocar for penetrating a vial stopper may be considered as a sharp device, especially if the spike is exposed and able to cause an accidental sharps injury. The International Health Care Worker Safety Center has computed that 590,164 needlestick and sharps injuries occur annually in the United States. “Sharps” boxes are often employed to collect used sharp devices like needles and scalpels. A user drops a sharp device into a sharps box immediately after use to prevent accidental sharps injuries like needle sticks that may result in transmission of disease and blood-borne pathogens. Sharps boxes generally have a small opening that prevents a hand from being inserted into the sharps box, and may not accept larger devices such as drug infusion cassettes.
Because drug cassettes are generally disposable and intended for single use, low manufacturing cost is desirable if an end product is to be competitive. Reduction of parts count may decrease inventory, cost of materials and assembly time, leading to lower manufacturing costs.
In certain situations, a disposable drug cassette may be used on the same patient with more than one drug vial. In those situations where multiple vial spikings will occur, a spike on a drug cassette has to reliably withstand repeated forces and stresses imposed upon it by multiple spiking cycles.
An ever-present concern with drug cassettes and drug infusion systems is “free flow” whereby drug in a vial, or residual drug in intravenous tubing, flows via gravity into a patient in an uncontrolled manner, especially in the case of potent drugs. Free flow of drugs is also possible even if a drug vial is not spiked on a cassette. Residual drug in an infusion line (peristaltic tubing and intravenous tubing) may flow by gravity to a still connected patient when a used cassette, without a vial, is being removed from a pumping unit. Air entrainment may also be possible in such a situation placing a patient at risk of air emboli in the bloodstream.
If an intravenous (IV) set is disconnected at the cassette end after a drug infusion and the same IV set is subsequently used for infusing fluid to the same patient, residual drug trapped in the IV line, between the cassette end and the IV cannula end, will be infused to the patient first. In the case of potent drugs, the residual drug may produce unexpected consequences such as drowsiness and/or loss of consciousness. If the patient has been transported after the drug infusion, for example, for a sedation and analgesia procedure, to another location where no resuscitation personnel or equipment is available and/or functioning, an unplanned clinical emergency may occur that may place the patient at risk.
Most IV infusion tubing sets use a manually-operated slide valve that is placed between a drug container end and an IV cannula end. A user of the infusion system has to remember to manually close the slide valve after an infusion so that free flow of residual drugs potentially followed by air entrainment does not occur upon disconnection of the IV line at the drug container end. If a slide clamp is placed upstream of the IV cannula end, then the slide valve, even if closed, cannot prevent air aspiration upon disconnection of the IV line at the IV cannula (patient) end. Thus, in conventional IV infusion tubing sets, disconnection at the IV cannula end would present a risk of air aspiration resulting in air emboli unless there is another stopcock or flow control component downstream at the IV cannula. A stopcock manufactured from a hard material such as plastic, when in close contact with a patient, may apply under certain circumstances, undue pressure to a patient's skin and tissues resulting in hypoperfusion, nerve injury or tissue damage.
Some drug cassettes incorporate peristaltic tubing held in position next to a rigid pressure plate on the cassette. One end of the peristaltic tubing is in fluid connection to a vial mounted on the drug cassette and the other end of the peristaltic tubing is in fluid connection to intravenous tubing that delivers fluid to a patient. A pumping mechanism, usually external to a drug cassette, presses rhythmically on the peristaltic tubing to pump the vial content and control its flow rate to the patient. The peristaltic tubing has to be held in place against the drug cassette pressure plate for accurate pumping action. In some existing designs, this is done with multiple metal clips that increase parts count.
Another potential failure mode during drug infusion may occur if peristaltic tubing is placed in the reverse orientation relative to a pumping unit, such that blood would be suctioned from a patient instead of drug being delivered to the patient. An indexing mechanism is generally used to prevent peristaltic tubing from being oriented in the reverse direction. This may be, for example, a mechanical part or component attached onto the peristaltic tubing with a corresponding, matching recess in a pumping unit when the peristaltic tubing is properly oriented. If the peristaltic tubing is improperly oriented, the mechanical indexing component will prevent mating of the peristaltic tubing to the drug cassette pressure plate and/or the pumping unit.
Re-use of drug cassettes may lead to cross-contamination by blood-borne pathogens. Prevention of accidental or deliberate re-use of used and contaminated drug cassettes is desirable from the point of view of patient safety.
Current vial entry mechanisms include metal spikes, such as, for example, metal-tipped spikes. Spikes that are designed for use with rigid walled containers like glass vials sometimes have two lumens, one for channeling flow of the vial content to a desired conduit and the other lumen for preventing buildup of vacuum above a meniscus of an inverted vial by allowing equilibration to atmospheric pressure.
Metal, or metal-tipped, spikes generally require less force to pierce a given vial stopper than plastic spikes. For an automated or semi-automated vial spiking system, higher spiking forces usually required by a plastic spike may lead to unreliable spiking action and in case of repeated uses (multiple vials used with a single cassette), high spiking forces may lead to failure of a plastic spike.
If a drug to be infused from a vial is capable of supporting bacterial growth such as the lipid emulsion used in propofol, a filter is used to trap airborne organisms and prevent them from entering into the vial, contaminating the drug, multiplying and harming a patient when the organisms are infused with the drug into the patient's bloodstream. The air filter generally comprises a filter media, a filter media holder and an external filter housing.